March 29, 2008
Now, one of the Brickmuppets crack team of science babes points out that, somewhat surprisingly, the numbers have already been run on this idea and it is quite doable.
The study, in pdf form here, is quite interesting and relevant to human exploration in ways that the ISS simply is not.
Designed as an exercise by a team of students from the University of Maryland (at College Park) the proposed Clarke Station is a manned, variable gravity research facility intended to determine exactly what gravity level is needed to sustain long term human health.
Given that all of the planets and moons with resources that make human settlement possible have substantially less gravity than Earth, this is a nontrivial question. Lunar Gravity can, of course, be tested on an off the shelf satellite...the moon...but it seems prudent to test physiological effects of other gravities at a location no farther than the moon where the bail and scramble back to earth time is measured in days not months (or years in the case of Titan). A variable gravity facility can of course be used for training in say, Martian gravity to learn any tricks and unwelcome surprises of a particular gravity level. It bears remembering that the 1/6th gravity of the moon required some considerable adaptation by the Apollo Astronauts to simply get around.
(boingy boingy boingy..)
We need to find out some very basic things....
Does gravity in the ballpark of the moon have the same long term effects as 0 gravity? If so, what is the lower limit of tolerable gravity? Can we have permanent settlements on the 1/4 g environment of Mars for instance? Can low gravity effects be mitigated by exercise or drugs in ways that actual free-fall cannot? (this seems likely....to a point....but we have no reference for where that point might be). What are the actual maximum rotation rates that a crew can reasonably adapt to? This has a big effect on how wide and therefore big and heavy the centrifuge habitat in a spacecraft needs to be I've see reports that suggest a 30 foot diameter is adequate (Zubrin referring to his Gaiashield mission) and some that say 100 feet or more is necessary....we need to KNOW this stuff.
None of this can be found out on the ISS or current spacecraft because they are in free fall. A proposed gravity deck on the ISS was omited for budgetary reasons (and I'm not sure it would have been useable by people). Manned space exploration is going to require these sorts of questions answered
The station is interesting for another reason. Its choice of radiation protection.
The station is positioned at a Lagrange point (L1) which leaves the crew without the protection of the Van-Allen belts. This is compensated for by filling the walls of the inflatable modules with water. A few trips will pump the water into the walls to give superb protection. The original NASA inflatable concepts (going back to the 80's) had this as a feature so it is well within the design parameters of the materials involved. Water is heavy, but it is easy to handle and is well tested as a radiation shield. Given the existence of an inflatable module, pumping in water is just one more thing that needs to be pumped, simplifying assembly. Outside cislunar space on a mission to another planet or an asteroid, this sort of rad shielding will be a real asset. This is not a new concept at all, and it is elegant in its simplicity but it has never actually been done.
The position of this station at a liberation point is of more significance now than it was when this plan was developed, as we now have as a national goal a return to the moon. As John Goff points out, orbital propellant depots at a Lagrange point have the double advantage of enabling greater payloads to be carried to the moon and learning important, practical hands on lessons about one of the primary technologies for spacefaring....transfering fuel and other fluids between spacecraft. More on this architecture here and here is Boeing's proposal, focusing not just on the nuts and bolts but its commercial viability...in this case of a low earth orbit facility. Things break, so if an orbital propellant depot is built having one of these nearby allows the crew to do double duty as gas station attendants!
It should be noted that the Bigelow-type inflatables are a fairly mature technology,for instance, here is a paper on inflatables from 1988.
Within the limits imposed by my stock disclaimer, this station seems to be a conservative and robust in design with a good fudge factor regards strength (it can sustain 1.2G) and the inflatable modules should simplify construction. It is a modest near term proposal using off the shelf technology that can bring in huge benefits There are certainly some issues not covered by these engineering students but in order to tweak those would only require NASA to send it to Langley or Glenn. All that would require would be for NASA to be looking seriously at this line of research.
And therein lies the rub.....
What is interesting about the inflatable space stations is not just limited to their "flexibility" (as far as being replaced, taking damage, etc.), but rather how much cheaper they may be compared to building the ISS ($100 billion and counting).
I think if Bigelow can prove that its stations are safe for human habitation, we may see the death of the ISS.
Posted by: Darnell Clayton at Mon Mar 31 12:32:53 2008 (Nplwn)
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